The invention relates to modular plastic conveyor belts and, more particularly, to two-material hinge pins for connecting consecutive belt rows together.
Because they do not corrode and are easy to maintain, modular plastic conveyor belts are widely used in many industries to convey articles. These belts, or chains, typically are constructed of a series of rows of one or more belt modules connected end to end into an endless conveyor belt. Each row includes spaced apart hinge elements at each end with apertures formed through the hinge elements. The hinge elements along one end of a row are interleaved with the hinge elements along an end of an adjacent row. The apertures of the interleaved hinge elements are aligned and form a passageway for a hinge pin. A hinge pin inserted in the passageway serves to connect the rows together and to allow them to pivot about the axis of the pin so that the belt can backflex or articulate about a drive sprocket. But rubbing contact between the hinge elements and the confined hinge pins causes both to wear. This wear is, of course, exacerbated in abrasive environments in which dirt and grit can make their way between the contact surfaces of the pins and the hinge elements.
Various techniques have been used to adapt modular plastic conveyor belts to abrasive conditions. For example, steel hinge pins are used to increase wear life. But steel pins are expensive and add significantly to the weight of the belt. As another example, soft urethane hinge pins have been used. But soft urethanes, while wear-resistant, do not make strong hinge pins as are required in all but extremely light-duty applications. Other solutions depart from using standard cylindrical hinge pins and instead use non-circular pins in the shape of flat strips that do not rotate relative to the hinge elements, but rather bend along their length as a living hinge. But these hinge pins must also be made out of a flexible material that does not offer much shear strength and is limited to use in lightly loaded applications. Furthermore, the apertures in the hinge elements must be shaped in a non-standard way to receive the hinge strips.
Thus, there is a need for a hinge pin that combines strength and abrasion-resistant properties for use in modular plastic conveyor belts operated especially in abrasive environments.
This need and others are satisfied by a hinge pin having features of the invention. The hinge pin for use in hingedly interconnecting adjacent rows of a modular plastic conveyor belt into an endless belt includes a rigid interior rod surrounded by a soft outer tube. The rod is preferably made of a rigid material, such as acetal, nylon, polypropylene, PVC, or steel, for high belt strength. The tube is preferably made of a soft urethane material. With the hinge pin journalled in passageways formed by aligned apertures in the interleaved hinge elements along adjacent rows of belt modules, the tube contacts the walls of the apertures. Testing has shown that the wear normally caused by the relative motion between the tube and the aperture walls is significantly less for a rod covered with a urethane tube. The combination of the strength of the rod and the natural abrasion-resistant properties of the urethane tube make for a strong, abrasion-resistant belt.